Wafer positioning method and apparatus

ABSTRACT

A method of correcting a misalignment of a wafer on a wafer holder and an apparatus for performing the same are disclosed. In an embodiment, a semiconductor alignment apparatus includes a wafer stage; a wafer holder over the wafer stage; a first position detector configured to detect an alignment of a wafer over the wafer holder in a first direction; a second position detector configured to detect an alignment of the wafer over the wafer holder in a second direction; and a rotational detector configured to detect a rotational alignment of the wafer over the wafer holder.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as, for example, personal computers, cell phones, digital cameras,and other electronic equipment. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductor layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flow chart of a method of detecting and correcting for amisalignment of a wafer on a wafer stage, in accordance with someembodiments.

FIGS. 2A, 2B, 3, 4, 5, 6, 7A, 7B, 8, 9, 10A and 10B are side views andtop-down views of intermediate stages in the method, in accordance withsome embodiments.

FIG. 11 is a plan view of an ion implanter, which may be used to performthe method, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Various embodiments provide an apparatus for detecting and correcting aposition of a wafer on a wafer holder in an ion exposure apparatus andmethods of using the same. The wafer may be loaded on the wafer holder.The wafer holder is connected to a wafer stage, which moves the waferholder and the loaded wafer relative to an ion beam used to perform anion exposure process on the wafer. After the wafer is loaded, the waferstage moves the wafer in an x-direction to determine an x-directionmisalignment of the wafer and moves the wafer in a y-direction todetermine a y-direction misalignment of the wafer. Lightemitter/detector pairs may be used to detect the x-directionmisalignment and the y-direction misalignment of the wafer. The waferstage shifts the position of the wafer and the wafer holder in order tocorrect for the detected x-direction misalignment and y-directionmisalignment of the wafer. The wafer stage performs a rotational scan inorder to determine a rotational misalignment of the wafer. The wafer mayinclude an alignment mark and a camera and/or light emitter/detectorpair may be used to detect the alignment mark, allowing for therotational misalignment of the wafer to be determined. The wafer stageshifts the rotational position of the wafer and the wafer holder inorder to correct for the detected rotational misalignment of the wafer.The wafer stage then tilts the wafer holder and the wafer to a desiredtilt angle and the ion exposure process is performed on the wafer.Correcting the position of the wafer to account for misalignmentsbetween the wafer and the wafer holder prior to performing the ionexposure process on the wafer improves within-wafer uniformity, reduceswafer-to-wafer process variations, reduces device defects, and improvesdevice performance.

FIG. 1 illustrates a flow chart of a method 100 for detecting andcorrecting a misalignment of a wafer on a wafer holder, in accordancewith some embodiments. The method 100 may be implemented in thefabrication of semiconductor devices. In some embodiments, the method100 may be implemented in an ion exposure apparatus. The method 100 maybe performed prior to exposing the wafer to an ion beam in an ionexposure process. The method 100 may include various detection andcorrection steps and may be performed in any suitable order. Althoughthe current application discusses the alignment apparatus and method inthe context of an ion exposure apparatus and an ion exposure process,the alignment apparatus and method may be used in any semiconductormanufacturing apparatuses and processes.

In step 101, a wafer is loaded on a wafer holder connected to a waferstage. The wafer stage may include one or more driving units, such asmotors, which may move, rotate, and tilt the wafer holder with respectto a major axis of an ion beam to be used during an ion exposureprocess. The wafer may be loaded on a top surface of the wafer holder,which may be parallel to the major axis of the ion beam. When the waferis loaded on the wafer holder, there may be misalignments between thewafer and the wafer holder, such as x-direction misalignments,y-direction misalignments, and rotational misalignments. Exposing thewafer to the ion beam without correcting for the misalignments betweenthe wafer and the wafer holder may result in uniformity issues acrossthe wafer, wafer-to-wafer process variations, device defects, andreduced device performance. As such, the position of the wafer may becorrected for misalignments prior to the wafer being exposed to the ionbeam.

After the wafer is loaded on the wafer holder, an x-direction scan isperformed in step 103 to determine the x-direction misalignment of thewafer on the wafer holder and a y-direction scan is performed in step105 to determine the y-direction misalignment of the wafer on the waferstage. Although the x-direction scan is illustrated and discussed asbeing performed before the y-direction scan, the x-direction scan andthe y-direction scan may be performed in any order.

The x-direction scan includes using the wafer stage to move the waferholder and the wafer in the x-direction, while using x-directionposition sensors to detect a first position of a first edge of the waferrelative to the wafer holder. The y-direction scan includes using thewafer stage to move the wafer holder and the wafer in the y-direction,while using y-direction position sensors to detect a second position ofa second edge of the wafer relative to the wafer holder. The x-directionsensors and the y-direction sensors may include obstruction sensors. Insome embodiments, the x-direction sensors and the y-direction sensorsmay each include a light emitter (e.g., a laser or the like) and a lightdetector (e.g., a photodetector or the like); however, any suitablesensors may be used. The x-direction sensors and the y-direction sensorsmay be located in specific fixed positions. The light detectors maydetect when the wafer blocks light emitted from the light emitters,which allows for positions of edges of the wafer to be detected. Thex-direction misalignment and the y-direction misalignment of the wafermay then be determined based on the detected position of the wafer andthe position of the wafer holder. In step 107, once the x-directionmisalignment and the y-direction misalignment of the wafer on the waferholder are determined, the wafer stage shifts the position of the waferholder in the x-direction and the y-direction in order to correct theposition of the wafer for the x-direction and y-direction misalignments.

In step 109, a rotational scan is performed in order to determine arotational misalignment of the wafer on the wafer holder. In someembodiments, the wafer may include one or more alignment marks, whichmay be used to determine the rotational position of the wafer withrespect to the wafer holder. In some embodiments, the alignment marksmay include notches which may be disposed in a sidewall of the wafer. Insome embodiments, the rotational scan includes capturing an image of thewafer using a camera and analyzing the image. The image may be analyzedin order to determine the position of the alignment mark, whichindicates the rotational misalignment of the wafer over the waferholder. In some embodiments, the rotational scan includes rotating thewafer holder, while using a rotational sensor to detect the position ofthe alignment mark. The rotational sensor may include a light emitterand a light detector. The light detector may detect light reflected fromsurfaces of the wafer and/or the wafer holder while the wafer and thewafer holder are rotated. Based on variation in the intensity,wavelength, or the like of light received by the light detector, theposition of the alignment mark may be determined. The rotationalmisalignment of the wafer may then be determined based on the detectedrotation of the wafer and the position of the wafer holder. Therotational scan may be performed by the camera and/or the rotationalsensor. The camera and rotational sensor may be located in specificfixed positions.

In step 111, once the rotational misalignment of the wafer on the waferholder is determined, the wafer stage shifts the rotational position ofthe wafer holder to correct for the rotational misalignment of thewafer. Although the rotational scan and correction are illustrated anddiscussed as being performed after the x-direction scan and they-direction scan and after the x-direction correction and they-direction correction, in some embodiments, the rotational scan and therotational correction may be performed before the x-direction scan, they-direction scan, the x-direction correction, and the y-directioncorrection or between any of the x-direction scan, the y-direction scan,the x-direction correction, and the y-direction correction.

Once the x-direction misalignment, the y-direction misalignment, and therotational misalignment of the wafer on the wafer holder have beendetermined and corrected, the wafer holder may be tilted before exposingthe wafer to the ion beam. For example, the wafer stage may tilt thewafer holder and the wafer such that major surfaces of the wafer holderand the wafer are perpendicular to an axis of the ion beam, or at aspecified tilt angle to the ion beam. Then, in step 113, the wafer isexposed to the ion beam in the ion exposure process. Correcting themisalignments between the wafer and the wafer holder prior to exposingthe wafer to the ion beam improves the uniformity of the ion exposureprocess across the surface of the wafer, reduces wafer-to-wafer processvariations, reduces device defects, and improves device performance.

FIGS. 2A through 10B illustrate side views and top-down views ofportions of an ion implanter during performance of the method 100. FIGS.2A, 3, 4, 5, 6, 7A, 9, and 10A illustrate side views and FIGS. 2B, 7B,8, and 10B illustrate top-down views. In FIGS. 2A and 2B, a wafer 205 isloaded on a wafer holder 203, which is connected to a wafer stage 201.The wafer stage 201 may include one or more driving units, such asmotors, which may be used to move the wafer holder 203 in thex-direction, the y-direction, and the z-direction, rotate the waferholder 203 around a central axis 204 of the wafer holder 203 andtilt/rotate the wafer holder 203 around a central axis 202 of the waferstage 201.

The wafer 205 may be loaded on a top surface of the wafer holder 203while the wafer holder 203 is in an initial position in an xy-plane. Thexy-plane may be parallel to an axis of an ion beam to which the waferwill subsequently be exposed. The wafer holder 203 may subsequently betilted to a yz-plane (e.g., a plane perpendicular to the axis of an ionbeam to which the wafer will subsequently be exposed), or at a tiltangle to the yz-plane prior to performing an ion exposure process on thewafer 205. In some embodiments, the wafer holder 203 may hold the wafer205 on a surface thereof using vacuum pressure, electrostatic forces, orthe like. The wafer holder may include heating and cooling mechanisms inorder to control the temperature of the wafer 205 during the ionexposure process.

The wafer 205 may include various material layers (e.g., dielectricmaterial layers, semiconductor material layers, conductive materiallayers, and/or the like) and/or IC features (e.g., dopedregions/features, gate features, interconnect features, and/or thelike), depending on the stage of IC fabrication in which the method 100is performed. The various material layers and IC features of the wafer205 may be formed over a substrate, such as a silicon substrate. In someembodiments, the substrate may include another elementary semiconductor,such as germanium; a compound semiconductor including silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; any other suitablematerial; or combinations thereof. In some embodiments, the substrate isa semiconductor-on-insulator substrate, such as a silicon-on-insulator(SOI) substrate, a silicon germanium-on-insulator (SGOI) substrate, or agermanium-on-insulator (GOI) substrate. Semiconductor-on-insulatorsubstrates may be fabricated using separation by implantation of oxygen(SIMOX), wafer bonding, and/or other suitable methods.

As illustrated in FIG. 2A, the wafer 205 may include an alignment mark207. In some embodiments, the alignment mark 207 may be a notch formedin a sidewall of the wafer 205 and may be used during the rotationalmisalignment scan and correction, discussed below with respect to FIGS.7A through 9 . In FIG. 2A, the alignment mark 207 is illustrated ashaving a triangular shape; however, the alignment mark 207 may have arectangular shape, a round shape, or any other suitable shape. Thealignment mark 207 may have a width W ranging from about 1 mm to about 4mm and a depth D from a sidewall of the wafer 205 ranging from about 1mm to about 4 mm. As such, the alignment mark 207 may be easilydetectable, without overly limiting the area of the wafer 205 occupiedby the alignment mark 207. In some embodiments, the alignment mark 207may be a reflective alignment mark, a high-contrast alignment mark, orthe like.

As illustrated in FIG. 3 , the wafer 205 may be loaded on the waferholder 203 with x-direction misalignments, y-direction misalignments,and rotational misalignments between a center point C_(W) of the wafer205 and a center point C_(H) of the wafer holder 203. The magnitude ofthe x-direction misalignments are represented as Δ_(x), the magnitude ofthe y-direction misalignments are represented as Δ_(y), and themagnitude of the rotational misalignments are represented as θ. A centerpoint C_(B) of an ion beam to which the wafer 205 is subsequentlyexposed may initially be set to the center point C_(H) of the waferholder 203. The steps illustrated in FIGS. 4 through 9 and discussedsubsequently are used to shift the position of the wafer 205 such thatthe center point of the ion beam is aligned with the center point of thewafer 205, thereby improving within-wafer uniformity, reducing waferprocess variations, reducing device defects, and improving deviceperformance.

In FIG. 4 , an x-direction scan is performed on the wafer 205 todetermine the x-direction misalignment Δ_(x). As illustrated in FIG. 4 ,the apparatus may include an x-direction light emitter 213, anx-direction light detector 214, a y-direction light emitter 215, and ay-direction light detector 216. The x-direction light emitter 213 andthe x-direction light detector 214 may collectively be referred to as anx-direction light emitter/detector pair and the y-direction lightemitter 215 and the y-direction light detector 216 may collectively bereferred to as a y-direction light emitter/detector pair. Thex-direction light emitter/detector pair and the y-direction lightemitter/detector pair may include obstruction sensors. In someembodiments, the x-direction light emitter 213 and the y-direction lightemitter 215 may include lasers or the like. In some embodiments, thex-direction light detector 214 and the y-direction light detector 216may include photodetectors or the like. Any suitable sensors may be usedfor the x-direction sensors and the y-direction sensors. The x-directionlight emitter 213, the x-direction light detector 214, the y-directionlight emitter 215, and the y-direction light detector 216 may be locatedin specific fixed positions. The x-direction light emitter 213, thex-direction light detector 214, the y-direction light emitter 215, andthe y-direction light detector 216 may be located in a plane parallel tothe xy-plane and major surfaces of the wafer 205 and the wafer holder203 when the wafer holder 203 is in the initial position.

The x-direction scan is performed by using the wafer stage 201 to movethe wafer holder 203 and the wafer 205 in the x-direction. Thex-direction light emitter 213 emits a light beam 217 (e.g., a laser beamor the like), which is directed towards the x-direction light detector214. As illustrated in FIG. 4 , the light beam 217 extends in adirection parallel to the y-axis. The x-direction light detector 214detects when the wafer 205 blocks the light beam 217 emitted from thex-direction light emitter 213. This indicates the edge of the wafer 205,from which the position of the wafer 205 in the x-direction may bedetermined. The x-direction misalignment Δ_(x) of the wafer 205 may thenbe calculated based on the position of the wafer holder 203 when theedge of the wafer 205 is detected.

In FIG. 5 , a y-direction scan is performed on the wafer 205 todetermine the y-direction misalignment Δ_(y). The y-direction scan isperformed by using the wafer stage 201 to move the wafer holder 203 andthe wafer 205 in the y-direction. The y-direction light emitter 215emits a light beam 219 (e.g., a laser beam or the like), which isdirected towards the y-direction light detector 216. As illustrated inFIG. 5 , the light beam 219 extends in a direction parallel to thex-axis. The y-direction light detector 216 detects when the wafer 205blocks the light beam 219 emitted from the y-direction light emitter215. This indicates the edge of the wafer 205, from which the positionof the wafer 205 in the y-direction may be determined. The y-directionmisalignment Δ_(y) of the wafer 205 may then be calculated based on theposition of the wafer holder 203 when the edge of the wafer 205 isdetected.

In FIG. 6 , the wafer stage 201 adjusts the position of the wafer holder203 and the wafer 205 in order to correct for the x-directionmisalignment Δ_(x) and the y-direction misalignment Δ_(y). Asillustrated in FIG. 6 , after the positions of the wafer holder 203 andthe wafer 205 are adjusted, the center point C_(B) of the ion beam isaligned with the center point C_(W) of the wafer 205 and both the centerpoint C_(B) of the ion beam and the center point C_(W) of the wafer 205are misaligned with the center point C_(H) of the wafer holder 203 bythe x-direction misalignment Δ_(x) and the y-direction misalignmentΔ_(y). Aligning the center point C_(W) of the wafer 205 with the centerpoint C_(B) of the ion beam prior to performing an ion exposure processimproves within-wafer uniformity, reduces wafer process variations,reduces device defects, and improves device performance.

FIGS. 7A and 7B illustrate a process for performing a rotational scan onthe wafer 205, in accordance with some embodiments. As illustrated inFIGS. 7A and 7B, a rotational camera 221 may be included over the wafer205 and the wafer holder 203. The rotational camera 221 may be locatedin a specific fixed position. The rotational camera 221 may be used tocapture an image of the wafer 205 and the wafer holder 203. The imagemay then be analyzed in order to determine the position of the alignmentmark 207 or any other identifying features on the surface of the wafer205. Based on the position of the alignment mark 207, the rotationalposition of the wafer 205 may be determined. The rotational misalignmentθ of the wafer 205 may then be calculated based on the rotationalposition of the wafer holder 203 and the rotational position of thewafer 205.

FIG. 8 illustrates an additional process for performing a rotationalscan on the wafer 205, in accordance with some embodiments. Theadditional process illustrated in FIG. 8 may be performed in additionto, or in place of the process illustrated in and discussed withreference to FIGS. 7A and 7B. As illustrated in FIG. 8 , the apparatusmay include a rotational light emitter 223 and a rotational lightdetector 224. The rotational light emitter 223 and the rotational lightdetector 224 may collectively be referred to as a rotational lightemitter/detector pair. The rotational light emitter/detector pair mayinclude obstruction sensors. In some embodiments, the rotational lightemitter 223 may include a laser or the like. In some embodiments, therotational light detector 224 may include a photodetector or the like.Any suitable sensors may be used for the rotational sensors. Therotational light emitter 223 and the rotational light detector 224 maybe located in specific fixed positions. The rotational light emitter 223and the rotational light detector 224 may be directed towards the topsurfaces of the wafer 205 and the wafer holder 203 at angles oblique tothe xy-plane and major surfaces of the wafer 205 and the wafer holder203 when the wafer holder 203 is in the initial position.

The rotational scan is performed by using the wafer stage 201 to rotatethe wafer holder 203 and the wafer 205. The rotational light emitter 223emits a light beam 227 (e.g., a laser beam or the like), which isdirected towards the wafer 205 and the wafer holder 203 and reflects offa surface of the wafer 205 or the wafer holder 203 towards therotational light detector 224. The rotational light detector 224 detectsa change in the reflected light beam 227 indicating the presence of thealignment mark 207. Based on the position of the alignment mark 207, therotational position of the wafer 205 may be determined. The rotationalmisalignment θ of the wafer 205 may then be calculated based on therotational position of the wafer holder 203 and the rotational positionof the wafer 205.

In FIG. 9 , the wafer stage 201 adjusts the rotation of the wafer holder203 and the wafer 205 in order to correct for the rotationalmisalignment θ. As illustrated in FIG. 9 , after the rotation of thewafer holder 203 and the wafer 205 are adjusted, the rotation of thecenter point C_(W) of the wafer 205 is aligned with the rotation of thecenter point C_(B) of the ion beam and both the rotation of the centerpoint C_(B) of the ion beam and the rotation of the center point C_(W)of the wafer 205 are misaligned with the rotation of the center pointC_(H) of the wafer holder 203 by the rotational misalignment θ. Aligningthe center point C_(W) of the wafer 205 with the center point C_(B) ofthe ion beam prior to performing an ion exposure process improveswithin-wafer uniformity, reduces wafer process variations, reducesdevice defects, and improves device performance.

In embodiments in which the rotational scan is performed aftercorrecting the x-direction misalignment and the y-direction misalignmentof the wafer 205, the wafer stage 201 may move the wafer holder 203 andthe wafer 205 in the x-direction and the y-direction while rotating thewafer holder 203 and the wafer 205 during both the rotational scan andthe rotational correction. Specifically, the wafer stage 201 may rotatethe wafer holder 203 and the wafer 205 rotate around the center pointC_(W) of the wafer 205. This keeps the center point C_(B) of the ionbeam aligned with the center point C_(W) of the wafer 205 and preventsadditional x-direction misalignments and y-direction misalignments. Insome embodiments, the rotational scan and/or the subsequent rotationalcorrection may be performed before the x-direction and y-direction scansand corrections. In embodiments in which the rotational scan and/or therotational correction are performed before the x-direction andy-direction scans and corrections, the wafer stage 201 may rotate thewafer holder 203 and the wafer 205 around the center point C_(H) of thewafer holder 203.

In FIGS. 10A and 10B, the wafer stage 201 rotates the wafer holder 203and the wafer 205 around the central axis 202 of the wafer stage and anion exposure process is performed on the wafer 205. The wafer stage 201may rotate the wafer holder 203 and the wafer 205 such that majorsurfaces of the wafer holder 203 and the wafer 205 are perpendicular toor at a tilt angle to a major axis of an ion beam 209 to which the wafer205 will be exposed. After the wafer 205 is tilted to an appropriateangle, the wafer stage 201 moves the wafer 205 in the x-direction andthe z-direction, such that the ion beam 209 exposes the entire surfaceof the wafer 205. The ion exposure process may be any suitable process,such as an ion etching process, an ion implantation process, or thelike. The ion beam 209 may be generated by an ion beam generator, whichmay include any number of an ion source, a mass analysis magnet, anaperture, a linear accelerator, a scanning unit, a converging unit, afinal energy magnet, an end station, and/or a controller.

Because the position of the wafer 205 on the wafer holder 203 iscorrected for any x-direction, y-direction, and rotational misalignmentsbefore exposing the wafer 205 to the ion beam 209, the entire majorsurface of the wafer 205 may be evenly exposed to the ion beam 209 for adesired exposure duration. This reduces within-wafer uniformity issues,reduces wafer-to-wafer process variations, reduces device defects causedby varied ion exposures, and improves device performance.

FIG. 11 illustrates an ion implanter 300, which may be used to exposethe wafer 205 to an ion beam 301 for the ion exposure process (e.g., anion implantation, an ion etching, or the like), in accordance with someembodiments. The ion implanter 300 may be used to direct the ion beam301 at the wafer 205 in order to perform the ion exposure process 113 ofthe method 100. As illustrated in FIG. 11 , the ion implanter 300 mayinclude an ion source 303, a mass analysis magnet 307, an aperture 311,a linear accelerator 313, a scanning unit 315, a converging unit 317, afinal energy magnet 319, an end station 321, a wafer stage 201(including a wafer holder 203), and a controller 327 to control theoperation of the ion implanter 300. Each of these pieces will bediscussed in the following paragraphs.

The ion source 303 may include a variety of components which are used togenerate an initial ion beam 305. For example, the ion source 303 mayinclude ion separation devices, ion acceleration devices, multiples orcombinations thereof, or the like. In some embodiments, the ion source303 may be an arc discharge ion source. The ion source 303 may generatethe initial ion beam 305 from various atoms or molecules, which mayinclude boron (B), aluminum (Al), gallium (Ga), indium (In), carbon (C),silicon (Si), germanium (Ge), nitrogen (N₂), phosphorous (P), arsenic(As), antimony (Sb), oxygen (O₂), fluorine (F₂), helium (He), argon(Ar), carbon monoxide (CO), carbon dioxide (CO₂), boron mono-fluoride(BF), boron di-fluoride (BF₂), boron tri-fluoride (BF₃), siliconmono-fluoride (SiF), silicon di-fluoride (SiF₂), silicon tri-fluoride(SiF₃), silicon tetrafluoride (SiF₄), phosphorous dimer (P₂), silane(SiH₄), methane (CH₄), combinations thereof, or the like. However, otheratoms or molecules may be used as the ion source 303 in someembodiments.

The ion source 303 may produce ions having a broad range ofcharge-to-mass ratios with only a certain narrower range ofcharge-to-mass ratios being suitable for the ion exposure process. Assuch, the initial ion beam 305 may be directed towards the mass analysismagnet 307. The mass analysis magnet 307 electromagnetically separatesthose ions having desired charge-to-mass ratios for the ion exposureprocess from those ions having undesired charge-to-mass ratios. Once acoherent ion beam 309 of ions having suitable charge-to-mass ratios isobtained, the coherent ion beam 309 may be sent to the aperture 311.

After the coherent ion beam 309 is obtained by the mass analysis magnet307, the coherent ion beam 309 passes through the aperture 311 in orderto further enhance and control the divergence of the coherent ion beam309. In some embodiments, the aperture 311 is an aperture with anadjustable width that can adjust the magnitude of the coherent ion beam309. For example, the aperture 311 may include adjustable and movableplates such that a spacing between the plates can be adjusted, therebyallowing for an adjustment of the beam current magnitude. Once thecoherent ion beam 309 passes through the aperture 311, the coherent ionbeam 309 may be sent to the linear accelerator 313.

The linear accelerator 313 may be used to impart additional energy tothe coherent ion beam 309 as it passes through the linear accelerator313. The linear accelerator 313 imparts this additional energy using aseries of electrodes (not separately illustrated) that generate anelectromagnetic field. When the coherent ion beam 309 passes through theelectromagnetic field, the electromagnetic field works to accelerate thecoherent ion beam 309. The linear accelerator 313 may include multipleelectromagnetic fields and may vary the electromagnetic fieldsperiodically with time or may adjust the phase of the electromagneticfields to accommodate ions with different atomic numbers as well as ionshaving different initial speeds.

Once accelerated, the coherent ion beam 309 is directed towards thescanning unit 315. The scanning unit 315 may be used to scan thecoherent ion beam 309 across the surface of the wafer 205. The scanningunit 315 may include at least a pair of horizontal electrodes and a pairof vertical electrodes for controlling horizontal scanning and verticalscanning of the coherent ion beam 309, respectively. In someembodiments, the scanning unit 315 may function to scan the coherent ionbeam 309 to cover the entire wafer width of the wafer 205. As discussedabove, the wafer stage 201 may be used to move the wafer 205 withrespect to the ion beam 301 in order to expose the surface of the wafer205 to the ion beam 301. As such, the scanning unit 315 may be omittedin some embodiments, or may be provided in addition to the wafer stage201.

After the coherent ion beam 309 is passed through the scanning unit 315,the coherent ion beam 309 is passed through the converging unit 317. Theconverging unit 317 may be utilized to modify the convergence anddivergence of the coherent ion beam 309, which may arrive from thelinear accelerator 313 to the scanning unit 315 as a substantiallyparallel beam. In some embodiments, the converging unit 317 includes oneor more (such as three) multipole lenses. The multipole lenses mayinclude a uniformity multipole lens, a collimator multipole lens,combinations thereof, or the like. However, any suitable number and typeof lenses may be utilized.

After the coherent ion beam 309 is passed through the converging unit317, the coherent ion beam 309 is passed through the final energy magnet319. The final energy magnet 319 may be used to remove ions and/orneutral particles that have been generated with undesired charge-to-massratios during the previous process of the ion implanter 300. The finalenergy magnet 319 may be similar to the mass analysis magnet 307 and mayelectromagnetically separate ions having desired charge-to-mass ratiosfor the ion exposure process from those ions having undesiredcharge-to-mass ratios.

After the coherent ion beam 309 is passed through the final energymagnet 319, the ion beam 301 is delivered to the end station 321. Theend station 321 may house the wafer stage 201, which handles the wafer205 which will be implanted with ions from the ion beam 301. The waferstage 201 is utilized to move the wafer 205 relative to the ion beam 301so as to expose the entire surface of the wafer 205 to the ion beam 301.As discussed above, the wafer stage 201 may include one or more drivingunits (not separately illustrated), which may be used to control theposition of the wafer 205 relative to the ion beam 301.

In some embodiments, the ion beam 301 may be delivered to the endstation 321 as a spot beam, which has a circular cross-section. In someembodiments, the ion beam 301 may be delivered to the end station 321 asa ribbon beam, which has a rectangular cross-section. The wafer stage201 and the scanning unit 315 may be used in conjunction to scan the ionbeam 301 across the surface of the wafer 205 such that a uniform iondistribution is achieved across the surface of the wafer 205. Asdiscussed previously, the position of the wafer 205 on the wafer holder203 of the wafer stage may be corrected prior to performing the ionexposure process, which further helps to ensure that a uniform iondistribution is achieved across the surface of the wafer 205. Thisreduces device defects, reduces device yield loss, and improves deviceperformance.

The controller 327 is used to control the operating parameters of theion implanter 300 during operation. The controller 327 may beimplemented in either hardware or software, and the parameters may behardcoded or fed into the controller 327 through an input port. Thecontroller 327 may be used to store and control parameters associatedwith the operation of the ion implanter 300, such as the desired ionbeam current, the current to the accelerator electrodes, and the like.Additionally, the controller 327 may also be used to control the waferstage 201 and, more specifically, the driving units of the wafer stage201, which, in turn, control the position, direction of movement, tiltangle, and the like of the wafer 205 with respect to the ion beam 301.

Embodiments may achieve advantages. For example, including thex-direction light emitter/detector pair, the y-direction lightemitter/detector pair, the rotational camera 221, and/or the rotationallight emitter/detector pair in the ion exposure apparatus allows for themethod 100 to be performed and for misalignments between the wafer 205and the wafer holder 203 to be corrected before performing an ionexposure process on the wafer 205. This improves the uniformity of theion exposure process across the surface of the wafer 205, reduceswafer-to-wafer process variations, reduces device defects, and improvesdevice performance.

In accordance with an embodiment, a semiconductor alignment apparatusincludes a wafer stage; a wafer holder over the wafer stage; a firstposition detector configured to detect an alignment of a wafer over thewafer holder in a first direction; a second position detector configuredto detect an alignment of the wafer over the wafer holder in a seconddirection; and a rotational detector configured to detect a rotationalalignment of the wafer over the wafer holder. In an embodiment, thefirst direction is perpendicular to the second direction. In anembodiment, the first position detector includes a first light emitterand a first light detector, and the second position detector includes asecond light emitter and a second light detector. In an embodiment, therotational detector includes a camera. In an embodiment, thesemiconductor alignment apparatus further includes an ion beam generatorconfigured to generate an ion beam, a major axis of the first lightemitter and a major axis of the second light emitter being in a planeparallel to a major axis of the ion beam. In an embodiment, therotational detector includes a third light emitter and a third lightdetector. In an embodiment, a major axis of the third light emitterextends through the plane parallel to the major axis of the ion beam atan angle oblique to the plane parallel to the major axis of the ionbeam.

In accordance with another embodiment, a method includes loading a waferon a wafer holder; performing a first scan to determine a firstmisalignment of the wafer with respect to the wafer holder in a firstdirection; performing a second scan to determine a second misalignmentof the wafer with respect to the wafer holder in a second direction; andshifting a position of the wafer holder in at least one of the firstdirection or the second direction to correct for the first misalignmentand the second misalignment. In an embodiment, the method furtherincludes tilting the wafer holder; and exposing the wafer to an ionbeam. In an embodiment, performing the first scan includes moving thewafer holder in the first direction and using a first laseremitter/detector pair to detect a first side surface of the wafer, andperforming the second scan includes moving the wafer holder in thesecond direction and using a second laser emitter/detector pair todetect a second side surface of the wafer. In an embodiment, the methodfurther includes performing a rotational scan to determine a rotationalmisalignment of the wafer with respect to the wafer holder; and rotatingthe wafer holder to correct for the rotational misalignment. In anembodiment, performing the rotational scan includes capturing an imageof the wafer with a camera and performing analysis on the image capturedby the camera to determine the rotational misalignment of the wafer withrespect to the wafer holder. In an embodiment, the wafer includes anotch in a side surface thereof, and performing the rotational scanincludes rotating the wafer holder and using a laser emitter/detectorpair to detect the notch. In an embodiment, the wafer includes a notchin a side surface thereof, performing the rotational scan includesrotating the wafer holder and using a laser emitter/detector pair todetect the notch, and performing the rotational scan further includescapturing an image of the wafer with a camera and performing analysis onthe image captured by the camera.

In accordance with yet another embodiment, a method includes loading awafer on a wafer holder; performing a rotational scan to determine arotational misalignment of the wafer with respect to the wafer holder;rotating the wafer holder to correct for the rotational misalignment;tilting the wafer holder; and exposing the wafer to an ion beam. In anembodiment, the ion beam is generated by an ion beam generator, and amajor surface of the wafer is parallel to a major axis of the ion beamgenerator while performing the rotational scan and rotating the waferholder. In an embodiment, performing the rotational scan includescapturing an image of the wafer with a camera and performing analysis onthe image captured by the camera to determine the rotationalmisalignment of the wafer with respect to the wafer holder. In anembodiment, the wafer includes a notch in a side surface thereof, andperforming the rotational scan includes rotating the wafer holder andusing a laser emitter/detector pair to detect the notch. In anembodiment, the method further includes performing a first scan todetermine a first misalignment of the wafer with respect to the waferholder in a first direction; performing a second scan to determine asecond misalignment of the wafer with respect to the wafer holder in asecond direction; and shifting a position of the wafer holder in atleast one of the first direction or the second direction to correct forthe first misalignment and the second misalignment. In an embodiment,the first scan is performed using a first light emitter/light detectorpair, and the second scan is performed using a second lightemitter/light detector pair.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor alignment apparatus comprising: a wafer stage; a wafer holder over the wafer stage; a first position detector configured to detect an alignment of a wafer over the wafer holder in a first direction, wherein the first position detector comprises a first light emitter and a first light detector; a second position detector configured to detect an alignment of the wafer over the wafer holder in a second direction; a rotational detector configured to detect a rotational alignment of the wafer over the wafer holder; and an ion beam generator configured to generate an ion beam, wherein a major axis of the first light emitter is in a plane parallel to a major axis of the ion beam.
 2. The semiconductor alignment apparatus of claim 1, wherein the first direction is perpendicular to the second direction.
 3. The semiconductor alignment apparatus of claim 1, wherein the second position detector comprises a second light emitter and a second light detector.
 4. The semiconductor alignment apparatus of claim 1, wherein the rotational detector comprises a camera.
 5. The semiconductor alignment apparatus of claim 1, wherein a major axis of the second light emitter is in the plane parallel to the major axis of the ion beam.
 6. The semiconductor alignment apparatus of claim 5, wherein the rotational detector comprises a third light emitter and a third light detector.
 7. The semiconductor alignment apparatus of claim 6, wherein a major axis of the third light emitter extends through the plane parallel to the major axis of the ion beam at an angle oblique to the plane parallel to the major axis of the ion beam.
 8. A method comprising: loading a wafer on a wafer holder; performing a first scan to determine a first misalignment of the wafer with respect to the wafer holder in a first direction, wherein performing the first scan comprises moving the wafer holder in the first direction and using a first light emitter/detector pair to detect a first side surface of the wafer; performing a second scan to determine a second misalignment of the wafer with respect to the wafer holder in a second direction; shifting a position of the wafer holder in at least one of the first direction or the second direction to correct for the first misalignment and the second misalignment; and exposing the wafer to an ion beam, wherein a major axis of the first light emitter/detector pair is in a plane parallel to a major axis of the ion beam.
 9. The method of claim 8, further comprising: tilting the wafer holder prior to exposing the wafer to the ion beam.
 10. The method of claim 8, wherein performing the second scan comprises moving the wafer holder in the second direction and using a second light emitter/detector pair to detect a second side surface of the wafer.
 11. The method of claim 8, further comprising: performing a rotational scan to determine a rotational misalignment of the wafer with respect to the wafer holder; and rotating the wafer holder to correct for the rotational misalignment.
 12. The method of claim 11, wherein performing the rotational scan comprises capturing an image of the wafer with a camera and performing analysis on the image captured by the camera to determine the rotational misalignment of the wafer with respect to the wafer holder.
 13. The method of claim 11, wherein the wafer comprises a notch in a side surface thereof, and wherein performing the rotational scan comprises rotating the wafer holder and using a light emitter/detector pair to detect the notch.
 14. The method of claim 11, wherein the wafer comprises a notch in a side surface thereof, wherein performing the rotational scan comprises rotating the wafer holder and using a light emitter/detector pair to detect the notch, and wherein performing the rotational scan further comprises capturing an image of the wafer with a camera and performing analysis on the image captured by the camera.
 15. A method comprising: loading a wafer on a wafer holder; performing a first scan to determine a first misalignment of the wafer with respect to the wafer holder in a first direction; performing a second scan to determine a second misalignment of the wafer with respect to the wafer holder in a second direction; shifting a position of the wafer holder in at least one of the first direction or the second direction to correct for the first misalignment and the second misalignment; after shifting the position of the wafer holder in the at least one of the first direction or the second direction to correct for the first misalignment and the second misalignment, performing a rotational scan to determine a rotational misalignment of the wafer with respect to the wafer holder; rotating the wafer holder to correct for the rotational misalignment; tilting the wafer holder; and exposing the wafer to an ion beam.
 16. The method of claim 15, wherein the ion beam is generated by an ion beam generator, and wherein a major surface of the wafer is parallel to a major axis of the ion beam generator while performing the rotational scan and rotating the wafer holder.
 17. The method of claim 15, wherein performing the rotational scan comprises capturing an image of the wafer with a camera and performing analysis on the image captured by the camera to determine the rotational misalignment of the wafer with respect to the wafer holder.
 18. The method of claim 15, wherein the wafer comprises a notch in a side surface thereof, and wherein performing the rotational scan comprises rotating the wafer holder and using a light emitter/detector pair to detect the notch.
 19. The method of claim 15, wherein the first scan is performed using a first light emitter/light detector pair, and wherein the second scan is performed using a second light emitter/light detector pair.
 20. The method of claim 19, wherein a major axis of the first light emitter/light detector pair is in a plane parallel to a major axis of the ion beam, and wherein a major axis of the second light emitter/light detector pair is in the plane parallel to the major axis of the ion beam. 